383 Overheating???

Gentlemen, I did a search for this and got alot of info, but wanted to start my own post with all my own pertinent information so that perhaps someone with the knowledge and expertise that I lack can chime in and give me the advice that I need to remedy my particular issue.

The problem I'm having is overheating at freeway speeds, hill climbing, or hard acceleration. The highest I've seen it get was 230 degrees when the ambient temperature was around 100 degrees. On average, when the ambient temp is somehwere in the 90's, it tends to run between 210-225 on the freeway. Anything lower than about 75 degrees ambient, and it seems to run great at about 180-200. I generally turn about 3k RPM at 80 mph and anything below 65 mph, it seems to run great at about 180-200. At an idle, it runs at 180 degrees all day long, regardless of the ambient temp. I'm not running a t-stat and installing one only made it worse. The engine is a 383 HP, bored .030 over, no clue how long ago it was rebuilt, but its definitely got low oil pressure at idle, so I'm guessing the bottom end is a little worn; it still makes plenty of power and doesn't smoke or burn oil. This issue has only presented itself after I made the following upgrades last spring. I first bolted a set of 440 source stealth aluminum heads onto it. Then I got rid of the mechanical fan and installed a Derale dual electric fan setup rated at 4600 CFM. This setup is bolted to an aluminum, 26", 2-row, top-bottom radiator that I was running before I had the overheating problems. I have since thinned the mix of h2o/ethlyene glycol from 50/50 to about 70/30, and that did help drop the temps all across the board about 10-20 degrees. I also have 2 bottles of purple ice in the mix. Its got a relatively new high volume water pump from summit in the original cast-iron housing. I bolted a brand new, Street Demon 750, electric choke, vacuum secondary carb onto it with 76's in the primary bowl and 83's in the secondary bowl. The distributor is the same mopar electronic ignition with the orange box that it was before the upgrades. I've adjusted the timing so I'm at about 15 degrees BTDC at an idle and about 35 degrees BTDC at 3k RPM. The only real anomoly that jumped out at me was that with the vacuum advance hooked up, the timing at 3k RPM wants to jump to like 60 degrees BTDC. However, I do not notice or hear any pre-detonation and the issue remains the same even if I disconnect the vacuum advance and again, this is the same distributor that I was running before I had the overheating issues. The plugs have a light brown coloration on the ground strap and elctrode, with light black soot on the threaded portion of the plug; indicating a rich idle and slightly lean condition under accleration. I'm in Sacramento, CA at near as makes no difference, sea level, but I drove it to Reno for Hot August nights and had the same issue at that elevation. It has never boiled over and it hasn't lost any coolant as far as I can tell; there is no white smoke or sweet smell from the exhaust, so I do not suspect a head gasket issue. I have not done a compression test or a leak down test, but might do that if anyone thinks either of those may be beneficial.

Hopefully, I haven't left anything out but if any of you think of anything that could possibly improve my situation, or have any questions, I would greatly appreciate some help. Thanks in advance.

You really need to install a thermostat. Install a 180* stat. what maybe happening with the Hi Volume water pump the coolant is flowing too fast through the radiator it's not getting cooled down.

1.Your fans should be pulling air through the radiator. (Not pushing as most think)2.Do you have a shroud around the fans?3.Where are you picking up your coolant temp? If from the cylinder head it will read 20* to 30* higher. Try taking the temp from the intake manifold.4.Try going a step colder in spark plug heat range. You don't want the aluminum head to detonate.5.Someone may have clearanced the engine for racing back then. They a 15/40 weight oil.6.Your transmission you didn't mention what you have.7.Plug color doen't sound out of the realm of things. As long as they are not blistered you should be Okay. 8.If your carb will tolerate it jump up .002 on your primary jets.I hope I touched on most of your problem.

As I said, I did install a t-stat, a 180* as a matter of fact, and all it did was speed up the rate of overheating. Instead of it taking 5-10 min on the freeway to jump to 225*, it only took a matter of seconds with a t-stat installed. The fans are indeed pulling air through the radiator and they do have shrouds cast as part of the fans. The coolant temp is coming from the water pump housing where it normally comes from on a big block, and since the intake manifold is dry on a big block mopar, I'm not sure where I'd get coolant temp from there. The cooler spark plug is a good idea, but I'm not experiencing any detonation that I can feel or hear, so I'm not sure if it will make any difference, but its worth a shot. Its got a 727 trans in it with the standard cooler lines that run to the bottom of the radiator. Thanks for the reply.

If it's getting hot at cruising speeds, that sounds like there is no air getting through the radiator. Are your Derale fans mounted in a shroud? If so, is the shroud solid, or are there places for the air to escape through it--besides the fan openings.

I have seen electric fan shrouds that completely encase the radiator, and while the car is driving, there is no way the air can go through the radiator, becasue it creates a dam effect.

Does it cool down after you stop driving and let it idle?
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Some people are like Slinkys; they're not very useful, but fun to watch when pushed down the stairs.

RBolig; that's precisely what I had suspected, as the fans are mounted in their own shrouds that cover roughly 80% of the suface area of the radiator and the ariflow exit is roughly the same size as each fan, so I'm guessing that at speed, there is roughly 25-30% of the radiator that is pretty well blocked by the shroud of the fans. Maybe more? However, I looked at the old mechanical fan shroud and it blocks roughly the same size area that the eletric fans shroud does, so how could that be making such a drastic difference? It definitely immediately cools down once I get off the freeway, almost instantaneously, within minutes on a hot day its back down to 180-200* in a matter of a few minutes. DrMopar; Yes, you are correct, 80 mph is illegal. However, the car does the same thing at 70 mph, which is legal in several areas here in the great state of California. The next time I need a lesson in local traffic laws, I will be sure to contact my local law enforcement. Until then, I would appreciate a focus on the issue I have outlined and not what traffic laws I may or may not be breaking. Thank you.

Does anyone think an electric water pump would help? I'm looking at one that bolts directly to the original cast iron housing and supposedly moves 50-55 GPM. Does anyone know what a belt driven pump moves per minute?

jclaus68:As I said, I did install a t-stat, a 180* as a matter of fact, and all it did was speed up the rate of overheating. Instead of it taking 5-10 min on the freeway to jump to 225*, it only took a matter of seconds with a t-stat installed. The fans are indeed pulling air through the radiator and they do have shrouds cast as part of the fans. The coolant temp is coming from the water pump housing where it normally comes from on a big block, and since the intake manifold is dry on a big block mopar, I'm not sure where I'd get coolant temp from there. The cooler spark plug is a good idea, but I'm not experiencing any detonation that I can feel or hear, so I'm not sure if it will make any difference, but its worth a shot. Its got a 727 trans in it with the standard cooler lines that run to the bottom of the radiator. Thanks for the reply.

I did read about the T-stats you had in it. Understand we are looking at things blind. I don't if the intake has a connection for a temperature gauge or not? If the water flows throught the radiator too fast it won't cool down. Its that simple.

You can be on the lean side of near detonation, thats another observation.

The fan shrouds are great another observation.

Just one thing OKAY now that I know you have an automatic. Try an indiviual trans cooler not connected to the radiator. Just the trans inself.

I know this will cook you a little, but try this. When your having this problem and the temp goes up turn the heater on full blast, give it some time. If the temp comes down you need more radiator, or someway to dissapate the heat. Be fair give it a try and see if that changes your engine temp.

Or how about this do you know the temp gauge is accurate?

You can try upjetting the carb. on the primary side at .002 intervales.

Unfortunatly thats the down side of electric fans. They take up a lot of area on the radiator.

225* is really not hot, when you consider the load on your engine.Why not try a seperate trans cooler, that may help bring the temp down.

If you were picking the temp up from the cylinder head the temp will be 20* to 30* higher....

Bob, thank you so much for your replies, I really do appriciate another view point on this as I really have banged my head against the wall so many times with this, any experience I can get from the minds pooled together here is immensely beneicial. I will definitely try the heater idea, that hadn't even occurred to me and if it solves the problem, a few minutes of suana like temperatures will be a small price to pay. As far as jetting, I've tried jetting it up a few sizes and it just seems to make it run rich, as in I can see black soot collecting around the exhaust. And the trans cooler is a good idea, I've considered that as well, but there again, I didn't need it before, I'm wondering why I would need that now where I didn't before.

I'll tell you I've been around this for 45 years. There is something that you might do or try and it goes to Chit on you. I always release the valve spring pressure when winter comes (I live in Mass.) I have big cams and very high valve spring pressure. I have 2 Race cars. My Camaro fired right up. My ChevyII would not start. I had put an MSD ign. that summer. It was ign. I had no spark. All I did was take the wires from the coil and really put them back on. The ChevyII fired right up. What did I?

Try the heater and sauna, putting a seperate trans cooler in will help your trans,and should help yout temp problem. There may also be a passage in the water jacket of one or both heads that will slow the cooling down. When you find the problem it will be something stupid...LOL...If you want PM me...I'll help you if I can.

i had the same problem with my 383 and it looked like my rad was flowing great but it was not it had heavy deposits i could not see .it only boiled over a couple of times and showed little sign of over heating with exception of run on from being so bluddy hot i was pulling my hair out trying to figure it out and finally took to a rad shop and when he pulled rad apart it was full of *** got a new 3 core with 3/4 inch tubes and problem solved.
dwayne venton

I had the sa e problem with my 69 charger, 383...I reassembled from timing change only to clean, paint and make things pretty. There was no theromstat in it so I put a 195 degree in it and it heated straight to 230+. So I took thermostat back out and drained some coolant out and filled with water, 70/30 I believe. So far she is holding well and hits around 210 when sitting at the drive through. I just bought the car a month ago, so I am still learning the ins and outs. Thank you to all foryour thoughts they truly helped.

This is the exact problem I have been having for years. I have done everything I know to do, and more. Except......change the radiator. It just seems to simple. I've got a 68 Superbee (http://www.youtube.com/watch?v=0puMjUtSV4I)and the heating issue is so bad I'm pretty much stuck to my neighborhood. I'm going to do the final steps, put highway gears on to lower the rpm and put the largest radiator I can get on it. If that doesn't work, I'm going to paint it pink and give it to my wife.